1. Field of the Invention
The present invention relates to connector assemblies for cardiac pacing leads, and more particularly to a connector assembly which readily connects with an in-line multielectrode pacing lead. The connector assembly is designed to be expandable to accommodate a plurality of electrical contacts on the pacing lead and is mounted in a soft, pliable, so-called pacer neck, which fits closely about the pacing lead to prevent fluid flow into the connector assembly and between the electrical contacts.
2. Description of the Prior Art
Pacing systems include a pacer, which comprises a metal container or case which contains electronic circuitry and a power supply, and a pacing lead. The proximal end of the lead is connected to output terminals of the pacer in a component of the pacer which is commonly referred to as the neck of the pacer mounted to a top side of the case.
Multiple electrode cardiac pacing leads are well known and have been utilized for pacing both the atrial and ventricular chambers of the heart. Such a pacing lead includes a multipolar electrode assembly at the distal end and terminal connectors or contacts at the proximal end. The multipolar electrodes at the distal end of the lead usually consist in a tip electrode and one or more ring electrodes along the length of the lead. Additionally, the lead may contain one or more sensors along its length which measure and monitor physiological parameters such as the partial pressure of oxygen or carbon dioxide within the chambers of the heart.
In a pacing system with one electrode on the pacing lead, the distal end of the lead contains the electrode and is usually placed in the ventricle of the heart. The electrode is connected to the lead by an insulated helically coiled wire. At the proximal end of the lead, a terminal pin is affixed to the lead. This pin is inserted into the pacer neck where it makes contact with a pacer lead connector which is in turn connected to the cardiac pacer circuit and power source.
With one electrode on the distal end of the lead, referred to as a unipolar system, one pacer lead connector is needed in the neck of the pacer. In this instance, the case or can of the pacer, which is normally metal, serves as an anode. In a bipolar system, where two electrodes are on the distal end of the lead, two pacer lead connectors are necessary in the neck of the pacer.
Currently, cardiac pacing systems focus upon the sensing of electrical signals generated by the myocardium or middle layer of either the atrial and/or ventricular chambers of the heart and the stimulation of one or both of these chambers in the absence of spontaneous electrical activity. In such a system, either two different leads are used or the lead used measures ventricular activity at its tip and atrial activity along its length and therefore, more than one connector is needed in the pacer neck. Here, in a unipolar system, two pacer lead connectors are required in the neck of the pacer; one for the atrial lead terminal and one for the ventricular lead terminal. In a bipolar system, four pacer lead connectors are required in the pacer neck to monitor both chambers of the heart.
Future pacing systems will include physiological sensors as part of the pacing lead or separate from it. These physiological sensors will measure parameters such as oxygen and carbon dioxide levels, pH or any combination thereof, to name a few. These parameters will be transmitted to the pacer circuitry for use in setting various pacer outputs. Additionally, each of these sensors will require an electrical contact within the pacer neck in addition to the contacts mentioned above for sensing electrical activity.
The type of multielectrode pacing lead or leads most suitable for this type of multilead and sensor system is a lead with multiple electrodes in an in-line arrangement. These leads allow the monitoring of several different parameters while only causing one insertion to be made into the heart which reduces trauma. An example of such a lead is disclosed in U.S. Pat. No. 4,469,104 which discloses a lead assembly for a body implantable tissue stimulator which contains a connector in the pacer neck which relies on a garter spring or an elastomeric conductive O-ring to contact the in-line electrode terminals at the proximate end of the lead. Although such a lead is effective, the connector used is hard to manufacture, does not maintain good electrical contact, is difficult to insert into and is too large to accommodate a large number of electrode terminals within the minute confines of the pacer neck.
Heretofore various connectors have been utilized for connecting the proximal end of a single or multielectrode pacing lead to the electrical outputs in the neck of a pacer. The most common type of connector employs a terminal pin on the proximal end of the pacing lead which is secured inside the connector of the pacer by a set screw. This arrangement is not completely desirable since it usually requires the surgeon to tighten the screw after the terminal pin of the lead is in place inside the neck of the pacer during implantation in a body. Such a procedure is complicated due to the small size of the screw and the conditions of the operating room.
Additionally the number of contacts for a multielectrode lead is restricted if a different set screw is needed for each electrode contact within the connector. Present connectors which employ such a set screw connector are limited to a maximum of 4 connectors due to the size limitations of the pacer neck.
Finally, this set screw also encounters problems with body fluids over an extended period of time which causes deterioration of the screw and entry of fluid into the electrical contact area causing damage and malfunction. In some instances, a cap has been used to cover the screw head but such a design has not been entirely effective and has further complicated the installation procedure.
Therefore, the need exists for a multiple contact connector or assembly in a pacer neck which is small in size, easy to manufacture, readily accommodates a multielectrode lead, is impervious to body fluids and can be adapted to receive numerous electrode leads which vary upon the number needed for each particular patient.
As will be described in greater detail hereinafter, the assembly of the present invention provides a device which is capable of readily accommodating an in-line multielectrode lead without any additional complex installation procedures and is completely sealed from the body in which it is implanted.
Moreover, the connector assembly of the present invention differs from the previously proposed connector assemblies and pacer neck constructions by providing a connector assembly and pacer neck construction which is small in size, contains its own strain relief for the lead end portion received therein, is easy to use, can accommodate a large number of electrode contacts, which are easy to manufacture, and which maintain high reliability of electrical contact throughout the life of the pacing system.